feat: add actions to FeedSource interface

Add listActions() and executeAction() to FeedSource for write
operations back to external services. Actions use arktype schemas
for input validation via StandardSchemaV1.

- ActionDefinition type with optional input schema
- FeedEngine routes actions with existence and ID validation
- Source IDs use reverse-domain format (aris.location, aris.tfl)
- LocationSource: update-location action with schema validation
- TflSource: set-lines-of-interest action with lineId validation
- No-op implementations for sources without actions

Co-authored-by: Ona <no-reply@ona.com>

packages/aris-source-google-calendar/src/google-calendar-source.test.ts

@@ -45,13 +45,15 @@ describe("GoogleCalendarSource", () => {
 	describe("constructor", () => {
 		test("has correct id", () => {
 			const source = new GoogleCalendarSource({ client: defaultMockClient() })
-			expect(source.id).toBe("google-calendar")
+			expect(source.id).toBe("aris.google-calendar")
 		})
 	})
 
 	describe("fetchItems", () => {
 		test("returns empty array when no events", async () => {
-			const source = new GoogleCalendarSource({ client: createMockClient({ primary: [] }) })
+			const source = new GoogleCalendarSource({
+				client: createMockClient({ primary: [] }),
+			})
 			const items = await source.fetchItems(createContext())
 			expect(items).toEqual([])
 		})
@@ -198,7 +200,9 @@ describe("GoogleCalendarSource", () => {
 
 	describe("fetchContext", () => {
 		test("returns null when no events", async () => {
-			const source = new GoogleCalendarSource({ client: createMockClient({ primary: [] }) })
+			const source = new GoogleCalendarSource({
+				client: createMockClient({ primary: [] }),
+			})
 			const result = await source.fetchContext(createContext())
 			expect(result).toBeNull()
 		})